This invention is concerned with the alkylation of aromatic compounds with alkenes. In particular it is concerned with the selection of catalysts to permit such reactions to proceed with a high degree of conversion and selectivity, i.e.: with a minimum formation of byproducts such as polyalkylated species and alkene dimers and trimers.
The catalyst art is a notoriously unpredictable field. A catalyst that works well in one application may fail completely in a closely related application. Similarly, minor changes in a catalyst, such as using a slightly different support, may dramatically alter the catalyst's activity or selectivity. Further, one must not look only at a single characteristic of a catalyst. For a catalyst to be commercially viable, it must have excellent conversion and selectivity (i.e.: low byproduct formation), a reasonable lifetime, and physical properties allowing it to withstand the rigors of commercial operations.
The alkylation of aromatic compounds with alkenes is known. For instance, U.S. Pat. No. 2,572,701 (1951; B. Corson, et. al.; Koppers Company, Inc.) discloses the alkylation of benzene with propylene to produce cumene, using liquid sulfuric acid as a catalyst. The use of liquid catalysts has obvious process difficulties in a commercial manufacturing situation.
Current commercial processes for the production of cumene from benzene and propylene use a solid phosphoric acid catalyst ("SPA"). The SPA is generally clay or diatomaceous earth which has been saturated or impregnated with phosphoric acid, formed into extrudates or spheres, and calcined. To maintain the activity of the SPA it is necessary to add 100 to 200 ppm water to the feed stream. However, this water leads to phosphoric acid leaching off of the SPA catalyst, causing costly downstream equipment corrosion. Further, the amount of water reaching the catalyst bed must be tightly regulated, as too little will result in coking, while too much will destroy the physical integrity of the catalyst. In either case, the catalyst will be rendered inactive.
The use of solid acid catalysts for acid catalyzed reactions is also known. U.S. Pat. No. 4,721,810 (1988; D. Hargis; Ethyl Corporation) teaches the alkylation of aromatic amines with ethers, in the presence of a B-subgroup metal oxide alkylation catalyst, preferably a Group IV-B metal oxide (preferably a titanium oxide) with or without a minor proportion of a Group VI-B (preferably a molybdenum oxide) or Group VIII (preferably an iron oxide) metal oxide. This reference does not address the problem of alkylation with alkenes.
U.S. Pat. No. 4,233,139 (1980; L. Murrell, et. al.; Exxon Research & Engineering Co.) discloses the use of a catalyst selected from the group consisting of the oxides of tungsten, niobium, and mixtures thereof, and tungsten or niobium oxides in combination with one or more additional metal oxides selected from the group consisting of tantalum oxide, hafnium oxide, chromium oxide, titanium oxide, and zirconium oxide, supported on an inorganic refractory oxide support for catalytic cracking. The abstract of this patent contains the word "alkylation" but in view of the teachings in the patent of dealkylation, this may be an error. In any event, there is no enabling support for the use of these materials for alkylation processes.
Japanese patent publication JP 61 183,230 (World Patents Index Acc. No. 86-255378139, priority date 85.01.12, publication date 86.08.15; Keishitsu Ryubun Sh) teaches the manufacture of 2,2,3-trimethylpentane by reacting butene(s) with isobutene over a super acid catalyst. The catalyst is prepared by treating zirconium hydroxide or zirconium oxide with a sulphate-radical-containing solution and heating. The acid strength of the catalyst (H.sub.o) is greater that -10.6. This reference does not address the alkylation of aromatic compounds. Moreover, the reaction it teaches is, in the instance of the alkylation of aromatic compounds with alkenes, a destructive side reaction. This reference would suggest that this class of catalyst not be used for alkylation with alkenes.
K. Arata and M. Hino, Synthesis of Solid Superacid of Tungsten Oxide Supported on Zirconia and its Catalytic Action, Proc.--Int. Congr. Catal., 9th, Volume 4, 1727-1734, disclose a solid superacid catalyst with an acid strength of Ho.ltoreq.-14.52. The catalyst is obtained by impregnating Zr(OH).sub.4 or amorphous ZrO.sub.2 with aqueous ammonium metatungstate and calcining. The catalyst was used for several reactions, including the acylation of aromatics with acetic and benzoic acids (specifically the acylation of toluene with benzoic anhydride). The catalyst is reported to be more stable than "sulfate-treated materials". The same authors report similar data in M. Hino and K. Arata, Synthesis of Solid Superacid of Tungsten Oxide Supported on Zirconia and its Catalytic Action for Reactions of Butane and Pentane, J. Chem. Soc., Chem. Commun., 1988, p. 1259-1260. This reference does not address alkylation reactions.
Chemical Abstracts 111:164488b, Alkylation of Benzene on Superacid Catalyst (M. Yamamoto, Kenkyu Holoku--Tokyotoritsu Kogyo Gijutsu Senta 1988, (18), 85-8) reports that the alkylation of benzene with methanol, n-hexene, n-decene, or ethyl ether with various superacid catalysts was carried out in a fixed bed type apparatus with a continuous flow system at atmospheric pressure. In the alkylation of benzene with methanol, Zr(OH).sub.4.H.sub.2 SO.sub.4 and Ti(OH).sub.4.H.sub.2 SO.sub.4 were active at low temperature, but were unstable at high temperature. In the alkylation of benzene with n-hexene, the yield of cumene depended on the calcination temperature of SbF.sub.5.SiO.sub.2.Al.sub.2 O.sub.3. The thermal cracking products of n-hexene were further cracked over superacid catalyst. In the alkylation of benzene with ethyl ether, ethyl benzene was produced at 80.degree. C. and the activity of NH.sub.4 F.HF.SiO.sub.2. Al.sub.2 O.sub.3 was stable at 200.degree. C.
Chemical Abstracts 107:58245c, Alkylation of Phenol and Pyrocatechol by Isobutyl Alcohol Using Superacid Catalysts (R. A. Rajadhyaksha and D. D. Chaudhari, Ind. Eng. Chem. Res. 1987, 26(7), 1276-80), teaches the use of perfluorinated sulfonic acid resin catalysts such as Nafion-H catalyst to alkylate phenol and pyrocatechol with isobutyl alcohol. The chosen catalysts were reported to be superior than equivalent loadings of 98% sulfuric acid.
Tanabe, Hattori, and Yamaguchi, Surface Properties of Solid Superacids, Critical Reviews in Surface Chemistry, Volume 1, Issue 1 (1990), pages 1-25, is a lengthy review article looking generally at solid superacid catalysts. It discloses the use of WO.sub.3 /ZrO.sub.2 for the acylation of toluene with benzoic anhydride and the skeletal isomerization of butane and pentane. In a different section the article discloses the use of SO.sub.4.sup.2- /TiO.sub.2 --ZrO.sub.2, SO.sub.4.sup.2- /ZrO.sub.2, and SO.sub.4.sup.2- /TiO.sub.2 for the alkylation of benzene with propylene. It was also noted that no activity was observed when these supports did not contain the SO.sub.4.sup.2- functionality.